US3495193A - Variable radio frequency attenuator - Google Patents

Variable radio frequency attenuator Download PDF

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US3495193A
US3495193A US587100A US3495193DA US3495193A US 3495193 A US3495193 A US 3495193A US 587100 A US587100 A US 587100A US 3495193D A US3495193D A US 3495193DA US 3495193 A US3495193 A US 3495193A
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winding
control
signal
input
windings
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Leopold A Harwood
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RCA Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/24—Frequency- independent attenuators
    • H03H7/25—Frequency- independent attenuators comprising an element controlled by an electric or magnetic variable
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F19/00—Fixed transformers or mutual inductances of the signal type
    • H01F19/04—Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range
    • H01F19/06—Broad-band transformers, e.g. suitable for handling frequencies well down into the audio range
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G1/00—Details of arrangements for controlling amplification
    • H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
    • H03G1/0035—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using continuously variable impedance elements
    • H03G1/0076—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using continuously variable impedance elements using galvanomagnetic elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/02—Multiple-port networks
    • H03H11/24—Frequency-independent attenuators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
    • H01F29/14—Variable transformers or inductances not covered by group H01F21/00 with variable magnetic bias
    • H01F2029/143—Variable transformers or inductances not covered by group H01F21/00 with variable magnetic bias with control winding for generating magnetic bias

Definitions

  • An active radio frequency attenuator circuit includes a transformer having an input, output, and control windings.
  • the signal to be attenuated is applied to both the input and control windings in such a manner that a signal is induced in the output winding which is proportional to the difference in amplitude between the signals coupled to the input and control windings.
  • Means are also provided for varying the amplitude of the signal applied to the control winding in ⁇ such a manner as to control the amplitude of the resultant signal produced in the output winding.
  • This invention relates to a device which provides a controlled attenuation of electrical waves. This invention has particular applicability in automatic gain control (AGC) circuitry.
  • AGC automatic gain control
  • AGC is typically provided by a voltage, derived from the detected signal, which was used to vary the amplification of the input and intermediate amplifying stages by changing the bias voltage applied to these stages.
  • This method is less useful at higher frequencies and in narrow band circuits, especially in transistor receivers.
  • variation of the operating point produces changes in the transconductance characteristic and input capacitance which respectively may give rise to such problems as cross modulation distortion and detuning of the input circuit. It is therefore desir able, especially in transistor receivers, to provide controlled attenuation at the antenna terminals to limit the dynamic signal handling requirements of the input circuitry. It is necessary that the attenuator have a low insertion loss and also be capable of low impedance design so that it may be easily adopted for use in antenna circuits which are generally of low impedance.
  • An object of this invention is to provide an improved device which variably attenuates electrical waves and particularly those at radio frequencies.
  • Another object is to provide an improved variable attenuator whose attenuation is a function of an applied control voltage.
  • Another object is to provide an improved variable attenuator which exhibits low insertion loss and is capable of efficient use in low impedance receiver input circuits.
  • An active radio frequency (RF) attenuator embodying the invention includes a transformer having three windings, where two are the input and output windings, and the third is a control winding.
  • the signal to be controlled is applied to the input winding and is also applied to the control Winding in such a manner that a signal is induced in the output winding which is proportional to the difference in amplitude between the signals coupled to the input and control windings.
  • the amount of the signal applied to the control winding is varied to control the amplitude of the resultant signal in the output winding.
  • FIGURE 1 is a schematic circuit diagram of a radio frequency attenuator embodying the invention
  • FIGURE 2 is a schematic diagram of an alternative circuit which may be connected between the terminals A and B of FIGURE l;
  • FIGURE 3 is a block diagram illustrating the use of radio frequency attenuators embodying the invention in a signal translating system.
  • the attenuator includes a transformer 14 having substantially unity coupled trilar windings which comprise respectively, an input winding 13, an output winding 16 and a control ⁇ winding 17.
  • the transformer 14 may includes three trililar close wound turns 0f 20 gauge wire wound around a flat ceramic ferrite core 15 which is 3A" long by 7/16 wide by 3/32 thick.
  • the control winding is positioned intermediate the input and output windings. The spacing between the windings is adjusted to determine the characteristic impedance, such as, for example, ohms which is suitable for coupling a 75 ohm signal source to a 75 ohm lead.
  • a signal source 11 is coupled across the input winding 13 by way of the pair of input terminals 12.
  • the signal source 11 is also coupled across the control winding 17 by way of a direct current blocking capacitor 20 and a transistor 21. Signal currents flow in opposite direction through the windings 13 and 17 and induce opposite and cancelling voltages in the output winding 16.
  • the collector electrode 22 of the transistor 21 is connected through a resistor 26 to a voltage source V, not shown, adapted for connection between the terminals 25.
  • the base electrode Z4 of the transistor 21 is connected through a resistor 23 to a control voltage terminal 27.
  • the control voltage which determines the amount an RF signal will be attenuated, may comprise an automatic gain control voltage. In the present instance, more attenuation of the RF signal is introduced as the control voltage ibecomes more positive. Thus, where the control voltage is an AGC voltage, it tends to become more positive as the level of signals from the source 11 increases.
  • ⁇ the control voltage is of -a value to cut olf the transistor f 21 thereby substantially blocking signal current iiow in :the contro-l winding 17.
  • signal current in the input winding 13 induces ⁇ a volt-age in the output winding 16 of substantial-ly the same amplitude as the input voltage.
  • the control vol-tage applied between termin-als 27 forward biases the base-emitter junc- -tion of the transistor 2-1 to reduce its dynamic collector resistance.
  • the voltage from the source V, the resistance of resistor 26 and the control voltage applied to the base elect-rode 24 are proportioned suc-h that the transistor 2'1 is operating in a saturate-d condition for maximum signal attenuation.
  • the particular values of these components establish the range of collector-to-emitter resistance for a -given range of control volta-ges.
  • FIGURE 2 illustrates a circuit including Ia PIN ⁇ diode 2S which functions as a variable resistance.
  • This circuit is inserted across terminals A and B in lieu of the transistor 21 shown in FIGURE 1.
  • a suitable type of PIN diode for this purpose is a 1N367, and comprises P and N type semiconductor regions separated by a region of intrinsic semiconductor mate-rial.
  • a control bias applied to this type of diode will vary its effective resistance 'over an extended range from about l0 ohms to a very high resistance.
  • An important feat-ure of this type 0f diode is its linear voltage-current characteristic which is necessary to achieve attenuation without the introduction of excessive cross modulation distortion,
  • the circuits employed in both of the embodiments shown work Well at VHF television frequencies.
  • Attenuators of the type described are also useful at UHF television frequencies. Approximate dimensions o-f the attenuator for UHF operation would be about three turns wound upon a 3/16" ferrite rod of about 1/2" in length. Also at those frequencies, a low capacity PIN diode would be used as described in connection in FIG. 2, but the general circuit would be unchanged.
  • FIGURE 3 shows a receiver circuit which illustrates the use of active attenuators as above-described.
  • the variable attenuator 31 may be employed between the antenna 30 an-d a tuner 32 which includes la radio frequency amplifier.
  • the attenuator itself may be a physical part of ⁇ an antenna input or impedance matching circuit. The attenuator in this position prevents overloading of the input amplifier stage and therefore reduces cross modulation distortion.
  • Another variable attenu-ator 33 is shown between the output -of the tuner 32 and .IF amplifier stages 34. This attenuator is used -to eliminate detuning of Vthe IF networks due to overloading at its input.
  • the control signal for the attenuator is -developed by the detector 35 fed into an AGC amplifier 37 through line 36. lt is then applied to an intermediate frequency ⁇ (IF) Iamplifier 34 and to the vari-able attenuators 31 and 33 and the tuner 32.
  • Delay mea-ns 38, 39 and 40 may be included, if desired, to control the time of application of the AGC voltages to the various amplifying stages and attenuators as a function of received signal levels.
  • a variable attenuation circuit comprising:
  • a transformer havin-g mutually coupled input, output ,and control windings said windings being Wound in a substantially trilar configuration to provide substantially unity coupling therebetween, with the -turns of the windings of said trifilar configuration being in a helical arrangement in spaced groups f three:
  • impedance means coupling said signal source to said control Winding so that signal currents flowing in said control winding induce signal volt-ages in said output winding of opposite polarity to said first polarity;
  • said impedance means is a PIN diode connected in series between said signal source an-d s-aid control winding, and including a direct voltage supply connected across said PIN diode for cont-rolling the impedance thereof.
  • said impedance means comprises la transistor having collector, emitter and base electrodes, said transistor collector and emitter elec-trodes being connected between ⁇ said signal source and said control winding, and control voltage means connected to said base electrode for controlling the collector-to-emitter impedance of said transistor.
  • a variable attenuator device for attenuating elec- Ytrical waves comprising:
  • a transformer having three mutually coupled windings, said windings being wound in a substantially trifilar configuration to provide substantially unity coupling therebetween, with the turns of the windings of said trifilar configuration being in a helical arrangement in spaced 4groups of three;
  • active circuit means electronically controlled and opperative to vary the amplitude of said Waves in one of said two windings such that the resultant wave induced into the third winding is proportional to the difference in amplitude between the electrical waves coupled to said two winding-s.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Power Engineering (AREA)
  • Networks Using Active Elements (AREA)
  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)
  • Circuits Of Receivers In General (AREA)

Description

- Feb. 10,1970 L. A. HARWO'O'D l 3,495,193 VARIABLE RADI FREQUENCY ATTENUA'YIOR Filed 0st. 17. 1966 @oA/ren 1@ .4 i
United States Patent O 3,495,193 VARIABLE RADIO FREQUENCY A'ITENUATOR Leopold A. Harwood, Somerville, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Oct. 17, 1966, Ser. No. 587,100 Int. Cl. H01p 1/22 U.S. Cl. 333-81 4 Claims ABSTRACT F THE DISCLOSURE An active radio frequency attenuator circuit includes a transformer having an input, output, and control windings. The signal to be attenuated is applied to both the input and control windings in such a manner that a signal is induced in the output winding which is proportional to the difference in amplitude between the signals coupled to the input and control windings. Means are also provided for varying the amplitude of the signal applied to the control winding in `such a manner as to control the amplitude of the resultant signal produced in the output winding.
This invention relates to a device which provides a controlled attenuation of electrical waves. This invention has particular applicability in automatic gain control (AGC) circuitry.
In the prior art AGC is typically provided by a voltage, derived from the detected signal, which was used to vary the amplification of the input and intermediate amplifying stages by changing the bias voltage applied to these stages. This method is less useful at higher frequencies and in narrow band circuits, especially in transistor receivers. In transistors, variation of the operating point produces changes in the transconductance characteristic and input capacitance which respectively may give rise to such problems as cross modulation distortion and detuning of the input circuit. It is therefore desir able, especially in transistor receivers, to provide controlled attenuation at the antenna terminals to limit the dynamic signal handling requirements of the input circuitry. It is necessary that the attenuator have a low insertion loss and also be capable of low impedance design so that it may be easily adopted for use in antenna circuits which are generally of low impedance.
An object of this invention is to provide an improved device which variably attenuates electrical waves and particularly those at radio frequencies.
Another object is to provide an improved variable attenuator whose attenuation is a function of an applied control voltage.
Another object is to provide an improved variable attenuator which exhibits low insertion loss and is capable of efficient use in low impedance receiver input circuits.
An active radio frequency (RF) attenuator embodying the invention includes a transformer having three windings, where two are the input and output windings, and the third is a control winding. The signal to be controlled is applied to the input winding and is also applied to the control Winding in such a manner that a signal is induced in the output winding which is proportional to the difference in amplitude between the signals coupled to the input and control windings. The amount of the signal applied to the control winding is varied to control the amplitude of the resultant signal in the output winding.
Other objects, features and advantages will appear from the drawings and descriptions hereinafter given. Referring to the drawings:
FIGURE 1 is a schematic circuit diagram of a radio frequency attenuator embodying the invention;
ICC
FIGURE 2 is a schematic diagram of an alternative circuit which may be connected between the terminals A and B of FIGURE l; and
FIGURE 3 is a block diagram illustrating the use of radio frequency attenuators embodying the invention in a signal translating system.
An active RF attenuator 10 suitable for operation over the VHF television band is shown in FIGURE l. The attenuator includes a transformer 14 having substantially unity coupled trilar windings which comprise respectively, an input winding 13, an output winding 16 and a control `winding 17. By way of example, the transformer 14 may includes three trililar close wound turns 0f 20 gauge wire wound around a flat ceramic ferrite core 15 which is 3A" long by 7/16 wide by 3/32 thick. As shown in the drawings, the control winding is positioned intermediate the input and output windings. The spacing between the windings is adjusted to determine the characteristic impedance, such as, for example, ohms which is suitable for coupling a 75 ohm signal source to a 75 ohm lead.
A signal source 11 is coupled across the input winding 13 by way of the pair of input terminals 12. In addition, the signal source 11 is also coupled across the control winding 17 by way of a direct current blocking capacitor 20 and a transistor 21. Signal currents flow in opposite direction through the windings 13 and 17 and induce opposite and cancelling voltages in the output winding 16.
The collector electrode 22 of the transistor 21 is connected through a resistor 26 to a voltage source V, not shown, adapted for connection between the terminals 25. In addition, the base electrode Z4 of the transistor 21 is connected through a resistor 23 to a control voltage terminal 27. The control voltage, which determines the amount an RF signal will be attenuated, may comprise an automatic gain control voltage. In the present instance, more attenuation of the RF signal is introduced as the control voltage ibecomes more positive. Thus, where the control voltage is an AGC voltage, it tends to become more positive as the level of signals from the source 11 increases.
lFor minimum attenuation of RF sign-als by the circuit 10, `the control voltage is of -a value to cut olf the transistor f 21 thereby substantially blocking signal current iiow in :the contro-l winding 17. Under `these conditions signal current in the input winding 13 induces `a volt-age in the output winding 16 of substantial-ly the same amplitude as the input voltage. To increase the attenuation of RF signals by the circuit 10, the control vol-tage applied between termin-als 27 forward biases the base-emitter junc- -tion of the transistor 2-1 to reduce its dynamic collector resistance. Under `these conditions signal current flows through the control winding 17 and ydevelops yfields which oppose the fields developed by the signlal currents flowing in the input winding 1.3. As `a result, Ia reduced -or attenuated `output voltage is developed across the output winding 1-6.
The voltage from the source V, the resistance of resistor 26 and the control voltage applied to the base elect-rode 24 are proportioned suc-h that the transistor 2'1 is operating in a saturate-d condition for maximum signal attenuation. The particular values of these components establish the range of collector-to-emitter resistance for a -given range of control volta-ges.
FIGURE 2 illustrates a circuit including Ia PIN `diode 2S which functions as a variable resistance. This circuit is inserted across terminals A and B in lieu of the transistor 21 shown in FIGURE 1. A suitable type of PIN diode for this purpose is a 1N367, and comprises P and N type semiconductor regions separated by a region of intrinsic semiconductor mate-rial. A control bias applied to this type of diode will vary its effective resistance 'over an extended range from about l0 ohms to a very high resistance. An important feat-ure of this type 0f diode is its linear voltage-current characteristic which is necessary to achieve attenuation without the introduction of excessive cross modulation distortion, The circuits employed in both of the embodiments shown work Well at VHF television frequencies.
Attenuators of the type described are also useful at UHF television frequencies. Approximate dimensions o-f the attenuator for UHF operation would be about three turns wound upon a 3/16" ferrite rod of about 1/2" in length. Also at those frequencies, a low capacity PIN diode would be used as described in connection in FIG. 2, but the general circuit would be unchanged.
FIGURE 3 shows a receiver circuit which illustrates the use of active attenuators as above-described. Because of its low impedance capability the variable attenuator 31 may be employed between the antenna 30 an-d a tuner 32 which includes la radio frequency amplifier. The attenuator itself may be a physical part of `an antenna input or impedance matching circuit. The attenuator in this position prevents overloading of the input amplifier stage and therefore reduces cross modulation distortion. Another variable attenu-ator 33 is shown between the output -of the tuner 32 and .IF amplifier stages 34. This attenuator is used -to eliminate detuning of Vthe IF networks due to overloading at its input. The control signal for the attenuator is -developed by the detector 35 fed into an AGC amplifier 37 through line 36. lt is then applied to an intermediate frequency `(IF) Iamplifier 34 and to the vari-able attenuators 31 and 33 and the tuner 32. Delay mea-ns 38, 39 and 40 may be included, if desired, to control the time of application of the AGC voltages to the various amplifying stages and attenuators as a function of received signal levels.
yWhat is claimed is:
1. A variable attenuation circuit comprising:
a transformer havin-g mutually coupled input, output ,and control windings, said windings being Wound in a substantially trilar configuration to provide substantially unity coupling therebetween, with the -turns of the windings of said trifilar configuration being in a helical arrangement in spaced groups f three:
mea-ns providing a signal source;
means coupling said signal source to said input winding so that signal currents flowing in said input winding induce signal voltage of a first polari-ty in said output Winding;
impedance means coupling said signal source to said control Winding so that signal currents flowing in said control winding induce signal volt-ages in said output winding of opposite polarity to said first polarity; and
4 act-ive circuit means electronically controlled and opperat-ive to vary the impedance `of said impedance mean-s to control the amplitude 'of sign-al currents Aflowing in said control winding.
2. The device as set forth in claim 1 in which said impedance means is a PIN diode connected in series between said signal source an-d s-aid control winding, and including a direct voltage supply connected across said PIN diode for cont-rolling the impedance thereof.
I3. The device as set forth in claim 1 in which said impedance means comprises la transistor having collector, emitter and base electrodes, said transistor collector and emitter elec-trodes being connected between `said signal source and said control winding, and control voltage means connected to said base electrode for controlling the collector-to-emitter impedance of said transistor.
4. A variable attenuator device for attenuating elec- Ytrical waves comprising:
a transformer having three mutually coupled windings, said windings being wound in a substantially trifilar configuration to provide substantially unity coupling therebetween, with the turns of the windings of said trifilar configuration being in a helical arrangement in spaced 4groups of three;
mea-ns coupling the electrical waves to be attenuated to two of said windings to develop mutually opposing fields;
active circuit means electronically controlled and opperative to vary the amplitude of said Waves in one of said two windings such that the resultant wave induced into the third winding is proportional to the difference in amplitude between the electrical waves coupled to said two winding-s.
References Cited UNITED STATES PATENTS 1,817,294 8/1931 Cutting et al. 333-24 2,808,474 10/ 1957 Maynard et al. 3,093,802 6/'1963 Chow 333-81 XR 3,168,715 2/1965 Woodworth S33-11 3,260,965 7/ 1966 Schmal.
OTHER REFERENCES Wide Band Transistor Variable Attenuators,
Watanabe et al., Proceedings of the IEEE, vol. 53, May 1965, TK 5700 I7 page 550.
hpa Application Note 904, The Pin Diode, Feb. 15, 1966, hp associates, Palo Alto, Calif., pages 1-16.
HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. `332-17
US587100A 1966-10-17 1966-10-17 Variable radio frequency attenuator Expired - Lifetime US3495193A (en)

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DE (1) DE1591420C3 (en)
GB (1) GB1195089A (en)
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SE (1) SE344146B (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3619786A (en) * 1966-12-30 1971-11-09 Texas Instruments Inc Solid-state vhf attenuator and tv receiver
US3631333A (en) * 1970-05-06 1971-12-28 Honeywell Inc Electrically controlled attenuator
US20080207153A1 (en) * 2005-10-28 2008-08-28 Seok Dong Choi Tuner
EP4322405A1 (en) * 2022-08-11 2024-02-14 Nxp B.V. Tunable attenuator

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1817294A (en) * 1928-03-16 1931-08-04 Cutting Fulton Electrical coupling system
US2808474A (en) * 1956-01-23 1957-10-01 Boeing Co Variable attenuation control circuits
US3093802A (en) * 1959-02-25 1963-06-11 Gen Electric Controllable signal transmission network
US3168715A (en) * 1962-06-27 1965-02-02 Gen Electric Trifilar wound hybrid transformer
US3260965A (en) * 1962-08-07 1966-07-12 Bell Telephone Labor Inc Variable impedance network employing a junction transistor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1817294A (en) * 1928-03-16 1931-08-04 Cutting Fulton Electrical coupling system
US2808474A (en) * 1956-01-23 1957-10-01 Boeing Co Variable attenuation control circuits
US3093802A (en) * 1959-02-25 1963-06-11 Gen Electric Controllable signal transmission network
US3168715A (en) * 1962-06-27 1965-02-02 Gen Electric Trifilar wound hybrid transformer
US3260965A (en) * 1962-08-07 1966-07-12 Bell Telephone Labor Inc Variable impedance network employing a junction transistor

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3619786A (en) * 1966-12-30 1971-11-09 Texas Instruments Inc Solid-state vhf attenuator and tv receiver
US3631333A (en) * 1970-05-06 1971-12-28 Honeywell Inc Electrically controlled attenuator
US20080207153A1 (en) * 2005-10-28 2008-08-28 Seok Dong Choi Tuner
EP4322405A1 (en) * 2022-08-11 2024-02-14 Nxp B.V. Tunable attenuator

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Publication number Publication date
DE1591420C3 (en) 1974-03-21
BE705168A (en) 1968-03-01
DE1591420B2 (en) 1973-08-23
NL6714026A (en) 1968-04-18
GB1195089A (en) 1970-06-17
DE1591420A1 (en) 1972-03-09
SE344146B (en) 1972-03-27

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